This invention relates to the construction or forming of a sheet metal or aluminum can shell and can end having a peripheral rim or crown which is double-seamed to the upper edge portion of a sheet metal or aluminum can body. Such a can end is formed from a drawn sheet metal can shell, for example, a shell produced by tooling as disclosed in applicant's U.S. Pat. No. 5,857,374 the disclosure of which is herein incorporated by reference. Commonly, the formed can shell includes a circular center panel which extends to a panel wall which extends to or also forms the inner wall of a reinforcing rib or countersink having a U-shaped cross-sectional configuration. The countersink is connected by a generally frusto-conical chuckwall to an annular crown which is formed with a peripheral curl. For beverage containers, the center panel of the shell is commonly provided with an E-Z open tab, and after the can body is filled with a beverage, the peripherally curled crown of the shell is double-seamed to the upper end portion of the can body.
When the can body is filled with a carbonated beverage or a beverage which must be pasteurized at a high temperature, it is essential for the can end to have a substantial buckle strength to withstand the pressurized beverage, for example, a buckle strength of at least 90 psi. Such resistance to “buckle” pressure and “rock” pressure is described in detail in U.S. Pat. No. 4,448,322, the disclosure of which is incorporated by reference. It is also desirable to minimize the weight of sheet metal or aluminum within the can end without reducing the buckle strength. This is accomplished by either reducing the thickness or gage of the flat sheet metal from which the can shell is drawn and formed and/or by reducing the diameter of the circular blank cut from the sheet metal to form the can shell.
There have been many sheet metal shells and can ends constructed or proposed for increasing the buckle strength of the can end and/or reducing the weight of sheet metal within the can end without reducing the buckle strength. For example, U.S. Pat. Nos. 3,843,014, 4,031,837, 4,093,102, above-mentioned U.S. Pat. Nos. 4,448,322, 4,790,705, 4,808,052, 5,046,637, 5,527,143, 5,685,189, 6,065,634, 6,089,072, 6,102,243, 6,460,723 and 6,499,622 disclose various forms and configurations of can shells and can ends and the various dimensions and configurations which have been proposed or used for increasing the buckle strength of a can end and/or reducing the metal in the can end. Also, published PCT application No. WO 98/34743 discloses a modification of the can shell and can end disclosed in above-mentioned U.S. Pat. No. 6,065,634. In addition to increasing the buckle strength/weight ratio of a can end, it is desirable to form the can shell so that there is minimal modifications required to the extensive tooling existing in the field for adding the E-Z open tabs to the can shells and for double-seaming the can shells to the can bodies. While some of the can shells and can ends disclosed in the above patents provide some of desirable structural features, none of the patents provide all of the features.